feat(FN-1862): add completion state tracking for onboarding

- Add markOnboardingCompleted() to set completedAt timestamp when user finishes onboarding
- Add isOnboardingCompleted() to check if onboarding was completed (vs dismissed)
- Update ModelOnboardingModal to call markOnboardingCompleted on successful completion
- Skip onboarding auto-open when already completed locally
- Add completion state tracking tests in ModelOnboardingModal.test.tsx
- Add model-onboarding-state unit tests
- Update useAuthOnboarding to check local completion state before auto-opening
- Document localStorage completion state tracking pattern in .fusion/memory.md

packages/dashboard/app/test/setup.ts

@@ -22,7 +22,7 @@ if (typeof window !== "undefined") {
 }
 
 // Mock fetch for project API tests
-const _originalFetch = globalThis.fetch;
+const originalFetch = globalThis.fetch;
 
 globalThis.fetch = vi.fn(async (url: RequestInfo | URL) => {
   const urlString = url.toString();